Atmospheric nitrogen deposition and its long-term dynamics in a southeast China coastal area

Abstract

Measurements were conducted during 2004–2005 and 2009–2010 to characterize atmospheric nitrogen (N) deposition to the Jiulong River Estuary – Xiamen Bay area in southeast China. Isotopic analysis and long-term data (1990–2009) for inorganic N extracted from the national acid deposition dataset were used to determine the dominant source of atmospheric nitrate and N component dynamics. The results showed that the mean dissolved total N concentration in rain water for the three coastal area sites was 2.71 ± 1.58 mg N L−1 (n = 141) in 2004. The mean dissolved inorganic N at the Xiamen site was 1.62 ± 1.19 mg N L−1 (n = 46) in 2004–2005 and 1.56 ± 1.39 mg N L−1 (n = 36) in 2009–2010, although the difference is not significant, nitrate turnover dominates the N component in the latter period. Total deposition flux over Xiamen was 30 kg N ha−1 yr−1, of which dry and wet deposition contributed 16% and 84%, respectively. Nitrate in wet deposition with low isotopic value (between −3.05 and −7.48‰) was likely to have mostly originated from combustion NOx from vehicle exhausts. The inorganic N in acid deposition exhibited a significant increase (mainly for nitrate) since the mid-1990s, which is consistent with the increased gaseous concentrations of NOx and expanding number of automobiles in the coastal city (Xiamen). The time series of nitrate anions and ammonium cations as well as pH values during the period 1990–2009 reflected an increasing trend of N emission with potential implication for N-induced acidification.